Structure of 4,4 '-dichlorobenzophenone: Implications for low temperature transport of triplet excitations

As inferred from our x-ray single-crystal diffraction data, the microscopic mechanism of the structural phase transition at 190 K in 4,4'-dichlorobenz ophenone is such that certain structural imperfections must be inevitably p resent in the low-temperature phase. These defects can be the physical caus e behind the shallow X-traps for triplet excitons. as observed in luminesce nce spectra.